😤 Hard 9×9 Sudoku

Free online hard Sudoku puzzle — 30%% cells filled. No login required.

About 9×9 Hard Sudoku

This is the classic 9×9 Sudoku grid with 30%% of cells pre-filled, leaving you with 70% to solve using pure logic. The 9×9 format consists of 81 cells arranged in 9 rows, 9 columns, and 9 sub-boxes — each must contain the numbers 1 through 9 exactly once.

At Hard difficulty, expect 30–60 minutes even for experienced players. This level is ideal for players who have solid Sudoku experience and want a genuine challenge requiring real technique.

💡 Pro Tip: You'll need pencil marks (Notes mode). Mark all candidates in every empty cell first, then systematically eliminate using the techniques below.

Solving Strategies for Hard Difficulty

To solve hard 9×9 Sudoku efficiently, use these techniques in order:

Pencil marks first: Enable Notes mode and fill all candidates before solving.
Naked pairs: Two cells in a row/col/box with identical two candidates — eliminate from others.
Pointing pairs: If a number only appears in one row/col within a box, eliminate it from that row/col elsewhere.
Hidden singles: Scan each unit for a number that can only go in one cell.

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Frequently Asked Questions

How many hard 9×9 puzzles are available?

Unlimited. Every time you click Play or New Game, a brand-new algorithmically generated puzzle is created. Our generator uses backtracking with MRV heuristic — you will never run out of unique puzzles.

Can I save my progress and resume later?

Yes. Your puzzle is auto-saved to your browser's localStorage every 15 seconds. Return within 24 hours on the same device and browser to resume exactly where you left off — including your pencil marks and timer.

Is this puzzle the same for everyone?

No — each puzzle is randomly generated uniquely for you. For a shared daily puzzle that's the same for everyone worldwide, visit the Daily Sudoku page.

Can I print this puzzle?

Yes. Visit the Printable Sudoku page to generate printable puzzles in any size and difficulty. 4 puzzles per page, save as PDF directly from your browser. No login needed.

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Free Hard 9×9 Sudoku — no login, no download, works on all devices.

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About 9×9 Hard Sudoku

The classic 9×9 Sudoku — 81 cells, numbers 1–9, nine 3×3 boxes. The most played format worldwide.

At Hard difficulty, 30% of the 81 cells are pre-filled, leaving 56 cells for you to solve. Requires careful technique and pencil marks.

Tip: Use the Notes feature to pencil in candidates for each empty cell before committing.

Other difficulty levels for 9×9

Questions

How many hard 9×9 Sudoku puzzles are available?

Unlimited. Every time you click "New Game" a brand-new algorithmically generated puzzle is created. You will never run out of puzzles.

Are these puzzles printable?

Yes! Visit our printable Sudoku page to generate 4 puzzles per page as a PDF. Free, no login needed.

What solving techniques does Hard difficulty require?

Naked/hidden pairs, pointing pairs, and advanced elimination.

Play Hard 9×9 Sudoku now

Free, instant, no login — works on mobile, tablet and desktop.

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